Jan. 3, 2012 -- Many popular ADHD medications have been in short supply, particularly less-expensive generics.

That's no surprise to people who've gone from pharmacy to pharmacy trying to fill their child's prescription -- or to those who've had to pay high prices for brand-name drugs to treat
ADHD (attention deficit hyperactivity disorder).

The drugs in question are stimulants that calm and focus people with ADHD. The shortages have affected the two main classes of ADHD drugs: methylphenidates and amphetamines.

Some popular drugs, such as Novartis'
Ritalin LA, are in short supply in some dosages but not in others. Other drugs, such as Teva's extended-release amphetamine, are on back order. Still others, such as Shire's
Adderall XR and its two "authorized generics" are in good supply, according to the FDA and the American Society of Health-System Pharmacists.

One reason for the shortage is extremely high demand for the drugs. While people with ADHD make up nearly all of the legitimate market, there's a huge demand for off-label and illicit use of stimulant drugs. Many companies say they simply can't keep up with this demand.

So why don't the companies simply make more ADHD drugs? One reason is that these drugs are controlled substances. The Drug Enforcement Administration (DEA) decides how much of each controlled substance the U.S. legitimately needs -- and then sets quotas on how much manufacturers can produce.

Since 2007, the U.S. has been limited to 50,000 kilograms of methylphenidate. The amphetamine quota went up to 18,600 kilograms in 2009. Several drugmakers have publicly stated that these constraints have limited their ability to meet demand.

"The DEA's point of view is there is plenty of the active ingredient out there," DEA spokeswoman Barbara Carreno tells WebMD. "The DEA is tasked with making sure there is enough for legitimate need without making so much (that) it is diverted for illicit purposes. So we try to ascertain the legitimate medical need in America and make sure there is enough out there to meet it."

Last month, the DEA announced that the 2012 quota for methylphenidate will increase to 56,000 kilograms, and the quota for amphetamine will increase to 25,300 kilograms. It remains to be seen whether these increases will ease ADHD drug shortages.

Shortage Points to Bigger Problem

The shortage of ADHD drugs is a symptom of a larger problem facing the nation's drug supply. Supplies of many different kinds of drugs are becoming hard to predict.

According to IMS, a medical informatics firm, more than 80% of drug shortages are generics. Cancer drugs are particularly likely to be in short supply. They made up 28% of all shortages in 2010 to 2011, the FDA reports.

But it's not just cancer. There have been short supplies of drugs to treat infections, heart disease, nervous system disorders, and pain, IMS reports.

In October 2011, the FDA issued a special report on drug shortages. Among its findings:

From 2005 to 2010, the number of drug shortages tripled from 61 to 178.

The leading reasons for drug shortages are problems at the manufacturing facility (43%), delays in manufacturing or shipping (15%), and shortages of the active ingredient (10%).